Annual report pursuant to Section 13 and 15(d)

Income Taxes - Summary of Reconciliation of Statutory Tax Expense to Actual Tax Expense (Detail)

v3.8.0.1
Income Taxes - Summary of Reconciliation of Statutory Tax Expense to Actual Tax Expense (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]      
Federal benefit at statutory rate of 34% $ (8,833) $ (4,109) $ (2,002)
State Taxes (Net of Fed. Benefit) 3    
Nondeductible expenses (154) 325 237
Recognized R&D tax credits   (418)  
Other credits generated   (58)  
Deferred rate change 3,346    
Change in valuation allowance 5,638 4,260 1,765
Total income tax $ 0 $ 0 $ 0